1. Field of the Invention
The present invention relates to an optical receiver receiving a light signal.
2. Description of the Related Art
The time of multimedia including the Internet has come. An optical communication network technique of backbone communication systems is desired to realize advanced services and broadband, and is actively developed toward information society. As the optical communication has a larger capacity and a higher rate, a receiver part in an optical transmission system is required to have further advanced receiving functions.
FIG. 15 is a view of a primary structure of the optical receiver. An optical receiver 100 is made up of an optical amplifier 101, a light receiving element 102, an amplifier 103, and a signal regeneration part 104.
The optical amplifier 101 receives a light signal transferred over an optical fiber cable, and amplifies it. The light receiving element 102 converts the amplified light signal into an electric signal, which is then amplified by the amplifier 103. The signal regeneration part 104 makes a decision as to the signal is “1” or “0” based on a fixed threshold so that the original signal can be regenerated.
However, the optical receiver 100 has the following disadvantages. The amplitude of the electric signal after the opto-electric conversion does not have a constant level but varies. The signal regeneration part 104 regenerates the original signal from the electric signal having the amplitude that varies by using a fixed optimal threshold level for decision making. The fixed threshold level is not always optimal to decision making on the amplitude-varying signal. This may result in errors in signal regeneration and degrades the quality of transmission and reliability.
The amplitude of the electric signal may be varied due to variation in the waveform of the input light signal, and variation in the opto-electric conversion efficiency resulting from the temperature dependence of the light-receiving element 102 and the amplifier 103.